The class implements roulette whell exploration policy. Acording to the policy, action a at state s is selected with the next probability:

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                  Q( s, a )
p( s, a ) = ------------------
             SUM( Q( s, b ) )
              b

where Q(s, a) is action's a estimation (usefulness) at state s.

Note:The exploration policy may be applied only in cases, when action estimates (usefulness) are represented with positive value greater then 0.